This invention relates to antennas for use in road vehicles.
Most vehicles today carry electronic equipment requiring an antenna. This requirement is currently exceeding the demands of simple FM and AM radio reception with rapid growth in the need for TV reception, satellite GPS reception for navigation systems, mobile phone antennas and future needs such as road toll collection, satellite phone, DAB, etc. Coupled with this increasing number of systems is a demand for xe2x80x98dynamicxe2x80x99 reception to overcome multipath and fading effects when mobile, at FM and TV frequencies in particular, requiring a number of antennas for diversity operation. Also there is pressure from the automobile stylists to integrate the antennas into the bodywork of the car so that the vehicle is aesthetically pleasing whilst also offering improved security and reliability of the antennas. In this application a screen antenna design concept is presented which aims to met these requirements, at least in its preferred embodiments.
A number of screen antenna designs are already available. For instance it has been proposed to use wire elements integrated with the heater grid or to modify the heater grid in order to provide a plurality of FM antennas.
The invention provides a road vehicle antenna comprising a slot defined by an aperture in an electrically-conductive structure of the vehicle body and a further electrically-conductive structure disposed within said aperture, the antenna having a plurality of antenna feeds electrically coupled to the slot, characterized by a said antenna feed being coupled to the slot at a position where a first excitation mode of the slot and at least one higher-order excitation mode of the slot each have a non-null value, and by control circuit means for controllably connecting a said feed or a combination of said feeds to a load so that in use the antenna exhibits a number of selectable radiation patterns in excess of the number of feeds.
The slot may be formed between eg. door boot or bonnet lid and its surrounding structure, or between a window frame (eg. a front or rear screen) and a conductive region or pattern in or upon the window glass, or some other body part having a conductive region, and its surrounding structure.
In the preferred embodiments, the basic approach is to capitalise on the heater grid (or corresponding electrically-conductive transparent film) which together with the window frame forms a slot around the periphery of the screen. This slot is excited using mode theory to form a number of coincident slot antennas and hence diversity operation.
We use mode theory to show such a slot can be excited in a number of ways to provide diversity, including having two antennas concurrently at FM and also providing antennas at other bands. The approach is not restricted to transparent conductive film but can be utilised with a conventional screen containing a heater grid.
The invention is in principle applicable to both receiving and transmitting antennas, and the claims are to be construed as extending to either or both.
Other features of the invention are set out in the subordinate claims, which are deemed repeated here as consistory clauses. Any of these features may be incorporated into the invention, singly or in combination, regardless of whether the current claim dependencies indicate such combination.
Other independent inventive aspects are constituted by any novel feature or combination of features, whether or not identified as such, disclosed in this specification which term includes the claims and drawings.
European Patent Application 0 760 537 A2 (Flachglas Automotive GmbH) discloses a vehicle window having an electrically-conductive coating and an antenna slot formed between at least one edge of the window and the coating. Two or more coupling devices may be spaced apart along the slot region for coupling radio-frequency waves out of the antenna.
The Handbook of Antenna Design; Volume 2; Editors: A. W. Rudge, K. Milne, A. D. Olver and P. Knight; pages 228 to 237, discloses a theoretical analysis of the radiation patterns of phased array antennas.